1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to a backlight driving method and a display apparatus using the same, and more particularly, to backlight driving method for adjusting the brightness of a backlight using a pulse width modulation (PWM) dimming method, and a display apparatus using the same.
2. Description of the Related Art
A liquid crystal display (LCD) display does not generally employ a self-radiating element, and thus requires a backlight to produce light.
One or more cold cathode fluorescent lamps (CCFL) are generally used as the light source of the backlight. The CCFL is operated in the range of normal glow discharge. The CCFL includes a sealed glass tube having an inner coating of phosphor. The sealed glass tube holds inert gases and a slight amount of mercury.
By adding high frequency waves between electrodes at both ends of the glass tube, glow discharge occurs in the low pressure mercury vapor. Mercury atoms, which are excited by the discharge, emit ultraviolet rays, and these ultraviolet rays excite the phosphor. A light is then radiated, with the wavelength corresponding to an energy difference, when the excited phosphor atoms return to the energy level of the ground state. Accordingly, the CCFL produce light in color representation according to the characteristics of the phosphor.
The CCFL is generally as thin as a wire and operates with low electric currents. The CCFL has many advantages such as low power consumption, low heat, high efficiency, and long life. Accordingly, CCFL has been widely adopted in the devices such as backlight for laptop computers, thin film transistor liquid crystal display (TFT-LCD), copier, and others.
Meanwhile, the CCFL has to have a dimming function, as well as switch on/off functions. The analog dimming, and pulsewidth modulation (PWM) (or, burst dimming), are mainly used to adjust the brightness of the CCFL.
The analog dimming adjusts the brightness, by adjusting the amplitude of a driving signal applied to the CCFL. The PWM dimming adjusts the brightness, by adjusting the pulsewidth of a PWM signal. The analog dimming is more convenient to use, but has a limited range of brightness adjustment. The PWM dimming provides a wider range of brightness adjustment, but may cause the overall operation of the inverter to be instable, due to repeated switching on and off
The LCD display drives CCFL according to a lamp current according the specifications. However, if the worst case applies to the initial driving of the lamp, for example, if cool start, or dynamic contrast ratio (DCR), applies, the CCFL is driven with an electric current lower than is prescribed by the specifications.
If this worst-case scenario happens, the mercury of the CCFL is not activated enough, resulting in malfunctions such as abnormality occurring in the color coordinates or flickering.
Accordingly, a method is required, to prevent a possible malfunction of a backlight, due to unsuccessful activation during an initial driving stage.